1. Field of the Invention
The present invention relates to brake shoes for bicycles, and more particularly to a brake shoe to be attached to the forward end of the brake arm of the bicycle.
2. Description of the Prior Art
Like the so-called caliper brake disclosed, for example, in Examined Japanese Patent Publication SHO 60-30854 and the so-called cantilever brake disclosed in Examined Japanese Patent Publication SHO 62-1813, brakes for bicycles generally comprise a pair of brake arms pivoted to the frame of the bicycle, and brake shoes attached to the forward ends of the respective brake arms and movable into pressing contact with the respective side surfaces of the wheel rim to exert a braking force thereon.
With reference to FIGS. 7 to 9, the brake shoe to be attached to the brake arm end comprises a shoe holder 3 having a connecting rod 2 on its back, and a rubber shoe block 4 fittingly held at its base portion by the shoe holder. The connecting rod 2 is attached to the unillustrated brake arm.
With the bicycle brake of the type mentioned, it is not suitable to attach the brake shoe 1 to the brake arm so that the braking face 4a will be in parallel to the rim 5 of a wheel as shown in FIG. 7, but it is favorable to attach the brake shoe as so inclined that the distance l1 between the front end of the braking face 4a and the rim 5 is smaller than the distance l2 between the rear end of the braking face 4a and the rim 5 as seen in FIG. 9. (The term "front" as used herein refers to the direction P of advance of the wheel rim 5 in rotation, and the term "rear" to the opposite direction.)
The reason is as follows.
When the brake shoe 1 attached to the brake arm as shown in FIG. 7 is pressed against the rim 5 in rotation, the frictional force exerted by the rim 5 on the braking face 4a in the direction of arrow P deflectively deforms the brake arm or the frame to which the arm is attached, shifting the brake shoe 1 to the phantom line position shown in FIG. 8. The braking face 4a of the shoe block 4 then will not be uniformly pressed against the rim 5 but the rear portion of the face 4a will be concentrically pressed against the rim 5 as seen in FIG. 8, possibly permitting the front portion of the braking face 4a to be out of contact with the rim 5.
Consequently, the braking face 4a of the shoe block 4 not only fails to apply an effective braking force on the rim 5 but is also likely to permit its rear portion to contact the rim 5 with poor stability and chatter, resulting in a markedly diminished braking force.
Accordingly, it is desired that the brake shoe 1 be attached, as positioned as shown in FIG. 9, to the brake arm, with allowance made for the deflection of the brake arm due to the frictional force to be exerted thereon by the rim on braking. When the brake shoe 1 installed in place is so positioned as shown in FIG. 9, the braking face 4a of the shoe block 4 becomes pressed against the rim 5 uniformly over the entire length of the face upon the application of the brake as the result of the deflection of the brake arm due to the frictional force applied by the rim. This enables the braking face to exert an effective braking force on the rim free of chatter.
For the reason given above, many of the brake shoe mounts of bicycle brakes are recently adapted to adjust the angle of inclination of the shoe block braking face 4a with respect to the rim 5.
Nevertheless, it is impossible for the user to accurately determine the inclination to be given to the braking face 4a relative to rim 5. Moreover, even if the proper angle of inclination is known, unskilled users will encounter difficulty in actually adjusting the braking face 4a to the preferred angle with respect to the rim.
Furthermore, the optimum inclination of the braking face 4a differs variously with the material of the shoe block, the coefficient of friction of the braking face 4a on the rim, or the estimated amount of deflection of the brake arm to be caused by the braking action. However, it is not always certain that the user will adjust the braking face to the desired inclination contemplated by the designer.